import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution4 {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @return int整型一维数组
     */
    public int[] inorderTraversal (TreeNode root) {
        // write code here
        Stack<TreeNode> s = new Stack<>();
        ArrayList<Integer> list = new ArrayList<>();
        if(root != null){
            s.push(root);
        }
        while(!s.isEmpty()){
            TreeNode cur = s.peek();
            if(cur.left != null){
                s.push(cur.left);
                cur.left = null;
            } else {
                s.pop();
                list.add(cur.val);
                if(cur.right != null){
                    s.push(cur.right);
                }
            }
        }
        int[] ret = new int[list.size()];
        for(int i = 0;i<ret.length;i++){
            ret[i] = list.get(i);
        }
        return ret;
    }
}